Underreaming method

Abstract

An underreamer which may be mounted on a core drill to allow single phase underreaming or creation of a bore hole of larger diameter beneath a pilot hole. A plurality of levers are powered by a plurality of corresponding jacks which are adapted to exert pressure on the levers in order to cause them to extend beyond the periphery of the expander body. Each lever contains at least one roller-cutter rotatably mounted to the lever so that when the levers are forced outward, the roller-cutters crush rock beyond the periphery of the expander body and thus underream the bore hole.

What is claimed is: 
     
       1. A process for sinking a bore of large diameter, comprising the steps of: a. providing an underreamer, comprising: (1) an expander body;   (2) a plurality of levers, each rotatably mounted to the expander body so it is adapted to rotate beyond the periphery of the expander body;   (3) a plurality of roller-cutters, each rotatably mounted to a lever; and   (4) a plurality of jacks, each mounted to a lever and adapted to apply pressure to the lever so as to force the roller-cutters against rock outside the periphery of the expander body;     b. attaching the expander body to a starter;   c. with the roller cutters of the underreamer folded inward, sinking a pilot hole approximately to the height of the roller cutters;   d. actuating the jacks to cause the roller cutters to underream the bore;   e. folding the roller cutters of the underreamer inward; and   f. repeating steps (c) through (e).   
     
     
       2. A process according to claim 1 further comprising the steps of introducing flush out fluid into the bore and using it to remove rock underreamed by the underreamer.